A novel pH-responsive wormlike micellar viscoelastic solution was constructed by a rosin-based anionic surfactant (Na-MPA-AZO-Na) in the presence of cetyltrimethylammonium bromide (CTAB). The viscoelasticity, aggregate morphology, and pH-responsiveness of the pH-responsive wormlike micelles have been investigated through the method of rheology and cryogenictransmission electron microscopy. Its corresponding mechanism has been studied using 1 H NMR and 1 H− 1 H 2D NOESY HNMR. The zero-shear viscosity (η 0 ) of the wormlike micellar solution rapidly decreases by 3 orders of magnitude as the pH increases from 5.21 to 9.56. The viscoelastic fluids and water-like solutions can be converted by tuning the pH between 3.62 and 12.00, and the corresponding aggregates also transform between wormlike micelles and spherical micelles. In addition, the wormlike micellar crosssectional diameter is approximately 10 nm, which is remarkably larger than that of the common wormlike micelles. The phenomenon can be attributed to the large steric volume of the rosin rigid skeleton. When the pH is 12.00, a "pseudo" Gemini surfactant is constructed by Na-MPA-AZO-Na and CTAB through the electrostatic interactions. Wormlike micelles also can be formed with the increasing concentrations. The η 0 of the wormlike micellar system shows strong dependence on concentration with an exponent of 9.6 (η 0 ∝ C 9.6 ). This work further promotes new applications of forest resources.
A novel rosin-based photoresponsive
anionic amphiphile, sodium N-azophenyl maleopimaric
acid imide carboxylate (AzoMPCOONa),
has been successfully synthesized. Its molecular structure was characterized
by 1H and 13C NMR and mass spectrometry (MS).
The photoisomerization of AzoMPCOONa was evaluated by ultraviolet
(UV)–visible spectrometry and 1H NMR. The structure
of AzoMPCOONa could be converted between the trans and cis isomers
by irradiation with UV/visible light. Importantly, a fascinating photoresponsive
viscoelastic solution was prepared by mixing AzoMPCOONa and cetyltrimethylammonium
bromide (CTAB). The properties of the photoresponsive viscoelastic
solution were further investigated by rheology, circular dichroism
(CD), and cryogenic transmission electron microscopy (cryo-TEM). Initially,
the AzoMPCOONa/CTAB system was a gel-like solution composed of entangled
wormlike micelles possessing the right-handed chiral structure. After
UV irradiation for 10 min, the gel-like solution transformed into
a slightly viscous solution, its zero-shear viscosity dramatically
reduced by 2 orders of magnitude, and the aggregates were converted
into rod-like micelles and spherical micelles. In addition, the right-handed
chiral structure of the aggregates disappeared. These dramatic changes
in the viscosity and the aggregate structure can be attributed to
the photoisomerization of the azobenzene group in AzoMPCOONa, which
led to changes in the molecular geometry and the packing parameter
of the AzoMPCOONa/CTAB system. Interestingly, the right-handed chiral
structure of wormlike micelles also is photoresponsive. The results
reveal the superiority of forest resources for preparing viscoelastic
solutions.
A highly water-soluble rosin-based surfactant (C 14 -MPA-Na) was synthesized. Novel temperature-responsive supramolecular hydrogels were further prepared using C 14 -MPA-Na. The microstructure and the mechanical properties of the hydrogels were investigated. Unexpectedly, instead of the long one-dimensional structure, a new kind of twisted semicircular aggregate was formed in the hydrogels, which was rarely reported. Besides, the hydrogels possessed excellent shear-recovery properties. Upon heating to 40 °C, the hydrogels transformed into viscoelastic solutions, which were constructed by worm-like micelles. By adjusting the temperature, the hydrogels and the viscoelastic solutions could be freely transformed. Nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy were used to further explore the possible self-assembly mechanism of C 14 -MPA-Na. The curved alkane chain which partially overlapped with rosin's rigid skeleton became stretched when heated to 40 °C. The introduction of the rosin rigid skeleton endowed the supramolecular hydrogels with a novel microstructure and contributed to the development of strategies for the utilization of forest resources.
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